If you are applying a side dress of a good fertilizer for the garlic, it may just be that they are not good producers. This can happen to most any seed or plant. A for instance- I start many pepper and tomato seeds in small pots indoors. They all get the same soil, light, watering, and fertilizers. Most do well, but a few are runts and don't ever seem to grow much beyond a few inches, no matter what I do. Usually, I don't plant the runts in my garen, but will transplant them into larger pots in hopes that they will grow more. I also add more fertilizer to them, but nothing seems to help. I would just chalk it up to a bad clove that hasn't produced well. If its common to a specific type of garlic, then , I would not plant that type again.
Good luck1

UncleJohn,
I just dug all my red stripe garlic and one row has 6 plants much smaller than the rest. They will stay until 50 % of the leaves dry and I will have 6 smallish bulbs to use in the kitchen or give away.
Yes, leave them to grow and you will have useable bulbs later.
Plant just the larger cloves and you will have fewer smalls.
Often the smaller plants produce "rounds".

I had 3 or 4 last year that never progressed beyond the single leaf stage. Initial thought was that they may have been from smaller cloves. When several simply vanished, I figured that something damaged the roots. This year, I've got at least 2 like that. Both are from varieties which are supposed to be large plants, one being Music. Only the largest cloves were planted but those plants are stuck with just one single long narrow spear; not a leaf and not a stem. Survival will be doubtful as they will both soon be shaded out by their companions.

Martin

I just had a disappearing leaf. The whole section of cloves had been complete (each had sprouted), and suddenly today, one was gone. I believe it was one of the laggards. I carefully dug down and found no signs of foul play, nor a clove.

John, I've got the same thing! When I got home this aft, went to check on the two odd ones. Both turned out to be Music and one had been a single leaf several days ago. Now it's laying on its side and apparently quite dead. The other has developed into a sort of broom. One main skinny spear and 3 smaller ones from the ground, but no stem. Of course, both are right in the center of the bed so I can't get at the one for an autopsy! Something damaged the plants between last fall and now. Why it's just in the Music row may indicate something in the genetics.

Martin